1. Field of the Invention
The present invention relates generally to the field of trauma medicine and wounds. More specifically the present invention relates to methods of enhancing wound healing and enhanced wound coverage materials.
2. Description of the Related Art
Burn injuries represent one of the most severe forms of trauma. The larger the burn injury, the more severe the consequences and the higher the chance of poor extended outcomes and death. There are over 2 million burn patients annually, and costs for treatment exceed one billion dollars a year. Fire and burn injuries are the third leading cause of injuries and death in children aged 1 to 18 years. The number of mortalities from burns has decreased over the last decade, primarily due to early and adequate fluid resuscitation, early and aggressive nutritional support, improved infection control, improved wound care/would healing, and hormonal modulation.
Wound healing is of major importance in the recovery of burn patients, and therefore, their clinical outcome. It has been shown that early wound excision and tissue grafting improved the hypermetabolic response and survival after burn injury. Autologous skin can be used to graft the excised wound (donor-site), however, this is not an effective treatment in patients with especially large burns. In these cases, synthetic skin materials or cadaver skin have been used.
Wound cover should be distinguished from wound closure. Wound closure materials are biologically accepted by the wound bed and become permanently incorporated into the healing wound. On the other hand, wound coverage materials rely upon incorporation into the wound coagulum and in-growth of granulation tissues for adhesion; this phenomenon is characteristic of many wound coverage materials. Wound coverage materials, in general, do not biodegrade, and therefore, can only be temporary substitutes for the epidermis. Wound coverage materials must therefore be replaced with the patient""s skin, either by re-epithelialization or skin grafts. In the case of temporary coverage, the wound should not be colonized with bacteria and should be sufficiently superficial that it would be expected to heal completely within 3 weeks. Epithelial cells from the epidermal appendages grow and replace the destroyed epidermis, and gradually, the wound coverage material is shed. Therefore, the primary goal for the wound coverage materials in superficial second degree burns are to limit the microbial invasion of the wound bed (microbial barrier) to thereby prevent infection, and to limit the access of air to thereby minimize pain.
Wound coverage materials have also been used for deep second-degree or third-degree injuries prior to definitive wound closure with autologous skin in patients with massive burn injuries. The optimal wound coverage material has yet to be determined. However, the requirements for wound closure materials are to mimic normal dermis and epidermis. Specifically, the requirements of a superior wound closure material are: a) to provide a nontoxic, antiseptic, noninflammatory, and nonantigenic barrier to bacteria and other microbes; b) to provide a normal rate of heat and water conductivity; c) to provide an immediate, uniform and intimate adherence to the wound bed; d) to provide support for normal local host defense and wound repair mechanisms; e) to maintain elasticity and long-term durability; f) to allow growth potential; and g) to provide long-term mechanical and cosmetic function with wound contracture properties that are comparable to split thickness autografts.
INTEGRA(trademark), ALLODERM(trademark) or BIOBRANE(trademark) demonstrate very good biocompatibility and healing characteristics. However, these materials are very expensive, which limits their widespread use. Cadaver skin is a relatively efficient and cheap approach for wound coverage. However, the risk of transmission of HIV, CMV, HSV and hepatitis is a significant concern, and therefore, limits application of cadaver skin.
Fetal membranes possess numerous advantageous characteristics which make this material applicable as wound coverage material, including: a) low immunogenicity; b) nontoxic, antiseptic and noninflammatory; c) no HIV, HSV or CMV infection; d) unlimited quantities (which, therefore, allow fetal membrane tissue to be an inexpensive alternative to existing skin replacements); e) variability of length, diameter and thickness; and f) endogenous mechanical components, such as collagen, laminin and fibronectin, to thus ensure mechanical stability, growth support and potential similar to that of normal human skin.
Biochemically, thermal injury is a particularly severe form of trauma accompanied by a hypermetabolic response characterized by high cardiac output, increased oxygen consumption, compromised immune response and protein and fat catabolism [34]. The burn wound supports this vulnerable hypermetabolic state by producing and releasing thromboxane and pro-inflammatory cytokines [35-37]. Wound healing is thus important to survival and recovery in burn patients [22,38-39]. Anabolic agents, such as growth hormone and insulin-like growth factor-I, have been shown to attenuate the hypermetabolic response and to improve wound healing [35,39-41].
Insulin-like growth factor-I, a small polypeptide approximately 7.5 kD in size, is an anabolic agent that has been shown to improve metabolism [35], gut mucosal function [42] and protein losses [43] after a thermal injury. IGF-I mediates the actions of growth hormone in the hypermetabolic state by attenuating lean body mass loss, the compromised immune response, the acute phase response, and by enhancing wound healing [35,38,44-47]. IGF-I treatment improves wound healing by stimulating collagen formation and the mitogenicity of fibroblasts and keratinocytes [40,41,48]. There are adverse side effects, such as hypoglycemia, mental status changes, edema, fatigue and headache, which limit the therapeutic utility of IGF-I in the treatment of burns [49,50]. These adverse side effects are most likely due to supra-physiological doses of free IGF-I, which are required for biological efficacy [49,50].
Selection of an appropriate vehicle for gene delivery is paramount [1,2]. Viruses, in particular adenoviruses due to their specific transfection capabilities, have been used as gene delivery vehicles [1-3]. Viruses, however, display viral infection-associated toxicity, immunological compromise, and possible mutagenic or carcinogenic effects that make this approach potentially dangerous [1]. Using liposomes as a delivery system thus becomes an attractive model due to their non-viral composition, stability, and ability to interact with the cell membrane [4]. The addition of cationic properties to the standard liposomal structure and incorporation of cholesterol, together with the use of cytomegalovirus (CMV) promoters into the cDNA constructs used for gene transfer, increase the efficacy and levels of transgenic expression equal to those achieved with adenoviral constructs [4,5].
The prior art is deficient in methods to enhance wound healing and enhanced wound coverage materials. The present invention fulfills this long-standing need and desire in the art.
The present invention describes a method of enhanced wound healing using liposomes carrying genes encoding growth-enhancing agents. The present invention further describes an enhanced wound coverage material impregnated with liposomes carrying genes expressing growth factors to improve wound healing. It is an object of the present invention to decrease the hypermetabolic response, and thus, improve the clinical outcome and increase the survivability after trauma, particularly thermal injury.
The present invention describes the incorporation of liposomal gene constructs directly into a wound and/or into the coverage material to improve wound repair and enhance the functionality of the wound coverage material. The present invention further describes the use of enhanced fetal human amnion membrane, in conjunction with liposomal gene constructs expressing growth factors, as a transient wound coverage material in full-thickness wound repair. Fetal membrane has advantages over currently used materials, such as Integra(trademark), Biobrane(trademark), Alloderm(trademark), and is an efficient and safe approach to improve clinical outcome.
One object of the present invention is to provide methods to enhance wound healing, methods to enhance wound coverage material and an enhanced wound coverage material.
In an embodiment of the present invention, there is provided a method of enhancing wound healing, comprising the step of: injecting into the wound a liposome, wherein the liposome comprises at least one gene encoding a growth-enhancing agent.
In another embodiment of the present invention, there is provided a method of enhancing wound healing, comprising the steps of: covering the wound with a wound coverage material, wherein the wound coverage material is impregnated with a liposome, wherein the liposome comprises at least one gene encoding a growth-enhancing agent.
In yet another embodiment of the present invention, there is provided a method of enhancing wound healing, comprising the steps of: covering the wound with a wound closure material, wherein the wound closure material is impregnated with a liposome, wherein the liposome comprises at least one gene encoding a growth-enhancing agent.
In still yet another embodiment of the present invention, there is provided an enhanced wound dressing, comprising: a wound coverage material; and a liposome comprising at least one gene encoding a growth-enhancing agent.
In another embodiment of the present invention, there is provided a composition for enhancing wound healing, comprising: a liposome, wherein the liposome comprises at least one gene encoding a growth-enhancing agent; and a pharmaceutically acceptable carrier.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention. These embodiments are given for the purpose of disclosure.